pandas读sql查询和读sql表的区别

问题描述

这两个命令在时间执行方面是否存在差异:

Is there a difference in relation to time execution between this two commands :

import pandas as pd

df=pd.read_sql_query('SELECT * FROM TABLE',conn)
df=pd.read_sql_table(TABLE, conn)

感谢您的帮助

推荐答案

我认为您不会注意到这种差异.

I don't think you will notice this difference.

这是两个函数的源代码:

Here is a source code for both functions:

In [398]: pd.read_sql_query??
Signature: pd.read_sql_query(sql, con, index_col=None, coerce_float=True, params=None, parse_dates=None, chunksize=None)
Source:
def read_sql_query(sql, con, index_col=None, coerce_float=True, params=None,
                   parse_dates=None, chunksize=None):
    pandas_sql = pandasSQL_builder(con)
    return pandas_sql.read_query(
        sql, index_col=index_col, params=params, coerce_float=coerce_float,
        parse_dates=parse_dates, chunksize=chunksize)

和

In [399]: pd.read_sql_table??
Signature: pd.read_sql_table(table_name, con, schema=None, index_col=None, coerce_float=True, parse_dates=None, columns=None, chunksize=None
)
Source:
def read_sql_table(table_name, con, schema=None, index_col=None,
                   coerce_float=True, parse_dates=None, columns=None,
                   chunksize=None):
    con = _engine_builder(con)
    if not _is_sqlalchemy_connectable(con):
        raise NotImplementedError("read_sql_table only supported for "
                                  "SQLAlchemy connectable.")
    import sqlalchemy
    from sqlalchemy.schema import MetaData
    meta = MetaData(con, schema=schema)
    try:
        meta.reflect(only=[table_name], views=True)
    except sqlalchemy.exc.InvalidRequestError:
        raise ValueError("Table %s not found" % table_name)

    pandas_sql = SQLDatabase(con, meta=meta)
    table = pandas_sql.read_table(
        table_name, index_col=index_col, coerce_float=coerce_float,
        parse_dates=parse_dates, columns=columns, chunksize=chunksize)

    if table is not None:
        return table
    else:
        raise ValueError("Table %s not found" % table_name, con)

注意:我有意切断了文档字符串...

NOTE: i have iintentionally cut off docstrings...

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